In the technique of isotope separation by laser induced, isotopically selective photoexcitation and ionization, laser radiation of desired frequencies is typically developed by amplifying and pulse combining the output of one or more master oscillators. These master oscillators are typically operated with an output frequency in the red-to-orange spectral region from the lasing of a flowing dye solution. A practical absorption frequency for exciting such a dye solution for lasing in the red-orange region lies in the green spectral range.
One technique employed to achieve the pumping or excitation radiation for a master oscillator under these circumstances is to employ the infrared radiation provided by the crystals of a YAG laser, which is of a frequency substantially lower than that required for master oscillator excitation in the green and to frequency shift the radiation by doubling its frequency through a second harmonic generator. The radiation passing through the crystal has both green and infrared frequencies. A laser cavity output mirror placed on the far side of the frequency doubling crystal can then be tuned to reflect the infrared while passing the green radiation for use in excitation of the master oscillator.
The output radiation pulses from such a master oscillator are preferably closely spaced in order to permit efficient amplifier operation and to reduce the possibility of amplifier self-oscillation.